Chronic back pain is a common disability in which spinal fusion surgery is sometimes beneficial. Far more functional outcomes would be obtained with a successful intervertebral disc prosthesis If commercialized world-wide, it has been estimated that disc prostheses would be implanted at a rate of one million per year, after five years of marketing with potential sales of two billion dollars. This SBIR Phase I project will perform research to develop a spinal device that will restore function of the spine and relieve back pain for patients with intervertebral disc degeneration. Dynamic Spine is pursuing the development of an intervertebral disc replacement. Historically, severe knee and hip degeneration were treated with fusion of the joint which decreased pain but eliminated motion. Currently, hip and knee fusion have almost been entirely eliminated due to the enormous success of prosthetic hip and knee replacements. For back pain due to disc degeneration that has not responded to nonoperative treatment, spinal fusion is recommended. Spinal fusion improves pain but limits motion and hence function, and also increases stress on neighboring discs which over time predisposes to additional disc degeneration. A successful disc replacement is not yet available. Dynamic Spine is developing a prototype disc replacement which is unique from others currently in development and has characteristics which should overcome deficiencies of other disc prototypes. A US patent has been obtained and international patents are pending. The objective of Phase I is to demonstrate that the device restores normal spine biomechanics (range of motion and stiffness) and is durable in fatigue testing.